How to extend an object in Scala with an abstract class with constructor?

Question

How to extend an object in Scala with an abstract class that has a constructor, and apply method of the object returns the object as subtype of the abstract?

for example :

abstract class AbstractResource(amount:Int) {
    val amount:Int
    def getAmount = amount
}


case object Wood extends AbstractResource{
    def apply(amount: Int) = {
        // something that returns the subtype
   }
}

I think a good solution is:

abstract class AbstractResource {
    val amount: Int = 0

    def getAmount = amount
}


case object Wood extends AbstractResource {
    def apply(quantity: Int) = {
        new AbstractResource {
            override val amount = quantity
        }
    }
}

But my problem is I can't edit AbstractResource

Are you sure you don't want case class Wood(amount: Int) extends AbstractResource(amount)? — Tobias Brandt
– Tobias Brandt, Commented Aug 7, 2013 at 8:06
Why does Wood have to extend AbstractResource? Note that the thing Wood#apply is returning is not of type Wood. — Tobias Brandt
– Tobias Brandt, Commented Aug 7, 2013 at 8:16
Well, then Wood must call the constructor of AbstractResource. I'm not sure what you're trying to achieve. — Tobias Brandt
– Tobias Brandt, Commented Aug 7, 2013 at 8:25
@Pooya How is this set of AbstractResource subtypes to be used? I have doubts that even your prototype solution is likely to achieve what you think it does, let alone what you actually need. — Shadowlands
– Shadowlands, Commented Aug 7, 2013 at 9:23

senia · Accepted Answer · 2013-08-07 08:38:01Z

5

I have no idea why should Wood extend AbstractResource, but this works:

class AbstractResource(val amount:Int) {
  def getAmount = amount
}

case object Wood extends AbstractResource(0) {
  def apply(amount: Int) = {
    new AbstractResource(amount)
  }
}

answered Aug 7, 2013 at 8:38

senia

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2 Comments

Pooya Over a year ago

I think I should use a middle abstract class

4lex1v Over a year ago

@Pooya what is a middle abstract class?

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